In 2025 ESA has started bistatic radar experiments between Mars Express (MEX) and the ExoMars Trace Gas Orbiter (TGO), to make the first attempts to localise areas of significant water at locations near the equator and at mid to low latitudes.

Building upon previous work, in this thesis an improved model to simulate bistatic reflectometry measurements between MEX and TGO was created. Moreover, at Earth GNSS-R (Reflectometry) measurements have been employed for several years, and concepts from GNSS-R were studied in this thesis and have been implemented into the model.

The simulated measurements were compared with measured data and with the model of the previous work. Measurement parameters, including signal polarization, s/c pointing, and permittivity were also investigated and the findings of this thesis show the effects that these parameters have on the received signal. Finally, future measurement opportunities were also investigated.

Mapping shallow subsurface water (ice) on near-equatorial Mars is critical for future (manned) exploration, yet existing research shows poor correlation, leaving its presence debated.

This thesis assesses dual-spacecraft Bi-Static Radar (BSR) measurement feasibility at Ultra High Frequency, providing near-global coverage ideal for comparison with gamma/neutron spectrometry hydrogen maps. The Mars Express lander relay antenna transmits a continuous signal probing a few metres into the subsurface (shallow depths which cannot be mapped by conventional low-frequency radar). The ExoMars Trace Gas Orbiter receives the echo, whose amplitude directly reflects permittivity variations induced by compositional changes, e.g. water (ice) deposits.

Models were created to optimize measurement planning and simulate the received power spectrum against BSR data. The current match is limited, reflecting the method’s novelty, and surface composition is yet to show a strong signature. However, after calibration, resolution increase and improving direct signal, seasonal and polarization effects modelling, reliable detections appear possible.

Space debris and micrometeoroids are abundant around our home planet and offer both an opportunity of research for scientists and a threat to human’s endeavours in space. Impacts with even the smallest particles can happen at such high velocities that they can damage or destroy an operational spacecraft, creating even more debris and possibly endangering its crew, if manned. Detecting and cataloguing the debris and micrometeoroid population has thus been a priority for many space agencies around the world to ensure safe space access. Unfortunately, small debris in high orbits cannot be detected by ground based observatories that can detect objects with a minimum diameter of 10 cm in LEO and 1m in GEO. This is why space based detectors are needed. Current detectors are small in size and can often detect only high velocity impacts due to relying on ionisation of particles upon impact. This MSc thesis investigated the possibility of using the whole spacecraft as a detector, by employing vibration sensors on its structure to detect impact-induced oscillations. These vibrations could contain information on the impactor’s mass, speed, material class and other features. Impacts of pieces of debris were simulated in a laboratory environment and the vibrations generated in a spacecraft-like structure were measured and processed to study the effectiveness of such a detection method. Three types of projectiles were used, beads of glass (3mm diameter, 0.04g average mass), teflon (3.2 mm average diameter and 0.033g average mass) and steel (3 mm average diameter and 0.11 g average mass). As target, to represent a spacecraft, a 3mm thick aluminium panel, a 5 mm thick aluminium- skin aluminium-honeycomb sandwich panel and a flight spare model of a solar array were used. An impact-location estimation algorithm was developed that can successfully determine the point of impact based on the signal of at least 4 sensors with centimetre accuracy. Analysis of the waveforms acquired by the sensors showed that deformation phenomena upon impact affect the frequency content of the signal, showing that to preserve as much as possible the high frequency content of the signal stiffer parts of a satellite are more indicated for this type of technology. Lastly, it was observed that the maximum voltage measured grows linearly with the momentum of the particles, making it possible to estimate the impact momentum solely based on the signal acquired. The dependence of voltage from the impact momentum together with the experimentally calculated coefficient of vibration dissipation of -0.05 cm^(−1) was used to determine the maximum distance of sensors from the point of impact as a function of particle speed and mass for successful detection of the impact. Particles as light as 0.03 g (the lightest used in the experiments) travelling at speeds as low as 15 m/s are expected to be detectable from sensors as far as 50cm, while for objects of 0.2 g travelling at speeds exceeding 200 m/s it is expected that a sensor can be as far as 1 meter away from the point of impact. The method, for its simplicity and low-cost provides an easy way to greatly increase the amount of data on small pieces of debris and micrometeoroid around our planet, enhancing space exploration safety and supporting future missions.

Since the first radio occultation measurements were performed to study planetary atmospheres, the calculations returning refractivity profiles always adopted the so-called "spherical symmetry assumption". This hypothesis imposes a null horizontal gradient of the atmospheric parameters within the region sampled during the occultation: a scenario that can be quite unrealistic for regions in proximity of the terminator line. This study suggests that another way of calculating refractivity profiles is doable, dropping the spherical symmetry assumption and assuming a straight line propagation of the radio signal through the atmospheric medium (which, according to the laws of refraction, should travel in a curved line, corresponding to the fastest trajectory according to Fermat's law). The study proved that the theoretical difference between the two methods is negligible (within 1%) and that numerical methods can be developed to account for the asymmetric regions within the atmosphere.